TRIGONTA. 
“J 
Or 
Section 2.—CiLAVELLAT®. 
TRIGONTA INGENS, Lycett, 1872. 
18 Lycett, p. 24, pl. viii, figs. 1—3. 
18 
72. 
77-9. Ibid., p. 207, pl. xxxvi, figs. 5, 6. 
1877. 
Triconta Keeprnatr, Lycett. Tbid., p. 196, pl. xxxv, figs. 1, 2. 
Remarks.—Maas' states that his 7. roelligiana, from the Gault of Wilhelmshéhe, 
near Langenstein, is related to 7. cagens ; but it seems to be clearly distinguished 
by the greater curvature of the ribs near the carina and the indistinctness or 
absence of tubercles. 
TL. Keepingi, Lycett, is known only by the two type specimens from the Spilsby 
Sandstone. I have carefully compared these with a large series of 7. ingens from 
the Claxby Ironstone—the chief horizon for that species, and find that the 
curvature and number of the coste and the size of the tubercles vary considerably 
in different specimens of 7’. ingens; some forms possessing smaller and more 
numerous tubercles agree perfectly, im these respects, with 7. Keepingi. The 
plications on the area of the smaller specimen of 7’. Keeping? are quite similar to 
those on 7’. ingens ; but on the larger specimen they are less distinct than usual ; 
this, I think, is accounted for by imperfect preservation. In comparing the form 
of the shell in the larger example of 7. Keepingi with that of 7. ingens it is 
important to note that that specimen is larger than usual, and that the whole of 
the marginal parts posterior to the umbo are very imperfect, so that a false idea 
may at first be taken of the height of the shell. Lycett’s figures, although giving 
a good idea of the character of the shell, are not accurate in either outline or size. 
Types.—T. ingens, from the Carstone of Downham, was formerly in the 
museum at Lynn, but cannot now be found. Specimens figured on Lycett’s plate 
xxxvi, from the Claxby Ironstone, are in the Museum of Practical Geology; and 
also a gutta-percha cast of the original of plate vin, fig. 1. 
1’. Keepingi, from the Spilsby Sandstone, in the Woodwardian Museum. 
Distribution—Spilsby Sandstone (zone of Pel. lateralis) of Claxby and 
Donnington. Claxby Ironstone (zone of Bel. lateralis) of Benniworth Haven. 
Carstone of Downham, Norfolk. 
The specimens named 1. Keeping’ are from the Spilsby Sandstone (zone of 
Bel. lateralis) of Claxby and Tealby. 
1 «Zeitschr. d. deutsch. geol. Gesellsch.,’ vol. xlvii (1895), p. 282, pl. ix, fig. 7. 
